import java.util.Scanner;

/**
 * Created by dllo on 3/30/18.
 */
public class Question01 {

    // 输入一个数字,求1+2+...+这个数字的和

    /*
    public static void main(String[] args) {

        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入一个数");
        int num = scanner.nextInt();

        int i = 0;
        while (i < num) {
            i++;
        }

        int sum = (1 + i) * i / 2;
        System.out.println("和为:" + sum);
    }
}
*/
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入一个数");
        int num = scanner.nextInt();

        int sum = 0;
        for (int i = 0; i <= num; i++) {
            sum = sum + i;
        }
        System.out.println(sum);
    }
}